1. Field of the Invention
The present invention relates to writing data onto and reading data from tape.
2. Background Art
Data is written onto tape for long term storage. In order to increase efficiency and stay competitive, makers of tape systems strive to increase data rates and tape storage capacities. The increase in storage capacity can be achieved by increasing both the linear data density and also the number of data tracks written across the width of the tape. However, as the track density is increased, systems which continue to utilize current head designs inevitably become limited by a number of fundamental dimensional constraints. One major issue is the finite dimensional stability of tape media. Due to pack compression, temperature, humidity, and the like, the tape width changes over time and with use.
Competitive data tape systems often use multiple read/write channels operating in parallel. This requires that tape storage system recording heads are constructed with multiple, independent, read-write structures which are laid out on a head substrate with a constant channel pitch between the structures. As tape width varies, the position of data tracks written on the tape changes relative to the position of the read and write elements fixed on the head. This may result in previously recorded data tracks becoming increasingly laterally displaced relative to the outer read-write elements on the head. In the limit of excessive dimensional changes, channels accessing read elements on the outer sides of the head are no longer able to read previously recorded data. This problem becomes increasingly important for very small track pitches expected in future tape drives. This problem also becomes worse as tape is made thinner due to the need to put increasing amounts of data within the given volume of a tape cartridge.
Typically, dimensional changes are mitigated by controlling, insofar as possible, the tape dimensional stability and by writing wide tracks which are read back using narrow data readers (i.e., “write wide-read narrow”). However, as the track density is increased in future products, such an approach will become increasingly problematic. This is due in part to the fact that the recording head read and write structures have a finite size (i.e., lateral width) largely determined by the photolithographic capability of tools used to define the write element coils and the requirement that the electric resistance of the coils is reduced as much as possible. In addition, reducing the physical separation of the write elements for adjacent tracks can also result in electrical coupling between the write elements which can result in corruption and loss of the written data. This is increasingly likely at the very signal high signal frequencies at which future drives will operate.
Although the tape dimensional stability of existing base film materials can potentially be improved, or other base film materials with improved dimensional stability used, this will significantly increase the cost of the tape with attendant reduced competitiveness when compared with other storage technologies.